The field of this invention is a crankshaft that is in modular form and more specifically relates to a connection technique that approaches the rigidity of a continuous crankshaft while allowing the flexibility to be in modular form.
Crankshafts are generally cast components that accommodate the required number of throws depending on the number of cylinders in the engine or compressor. In large compressor applications, a breakdown can be very expensive for the operator in the form of lost production or other process outage until repairs can be made, for instance. When the repair involves a crankshaft, the downtime can be lengthy because vendors seldom maintain an inventory of replacement crankshafts. Instead, when a replacement crankshaft is desired, it is manufactured from scratch, which can lead to delays and undesired downtimes.
One way to address the variety in the number of throws is to create a modular design where basic components can be assembled to each other to create the requisite configuration for a particular installation. The issue that doing this raises is how to fashion a connection that will be sufficiently rigid to address issues such as alignment, relative rotation and vibration, among other issues. Prior designs have attempted to connect modules with a splined male into female connection, as is described in U.S. Pat. No. 5,537,971. The problem with this design is the bulkiness of the connection and the clearances in the splined connection that permit assembly but over time can wear to the point of permitting relative rotational movement that can cause vibration and even spline failure, for example. Another solution is depicted in U.S. Pat. No. 4,622,864. This technique freezes a pin and inserts this frozen pin into aligned bores to put the modules together. This process requires precise alignment of the pin to make sure that lubrication passages through it are not obstructed. In other respects, modular shafts that attach the modules together with threads are known, as shown in a rock breaking tool in U.S. Pat. No. 4,657,306.
Therefore, there exists a need for improved modular crankshaft connection techniques.